Exposure method and apparatus, and device manufacturing method

ABSTRACT

An exposure apparatus includes a light source, one or two or more housings each for accommodating therein an optical element disposed along an exposure light path extending from the light source to a substrate, a first substitution system for substituting the interior of the housing with an inert gas ambience, and a second substitution system for substituting the interior of a holding mechanism for holding the optical element accommodated in the housing, with an inert gas ambience. The structure enables reduction in time for substitution of the exposure light path with an inert gas, and assures enlargement of a throughput of the exposure apparatus.

This application is a continuation application of application Ser. No.09/426,132, filed on Oct. 25, 1999 now U.S. Pat. No. 6,522,384.

FIELD OF THE INVENTION AND RELATED ART

This invention relates generally to an exposure apparatus for projectingand printing a circuit pattern formed on a mask, onto a substrate beingcoated with a photosensitive material, in a reduced scale. Moreparticularly, the invention is concerned with an exposure apparatuswhich uses deep ultraviolet light or an excimer laser as an exposurelight source.

Reduction type projection exposure apparatuses are used in a process ofmanufacturing a semiconductor device which is formed with a very finepattern such as LSI or VLSI. Miniaturization of a pattern has beenrequired strongly due to increases in the integration density of asemiconductor device, and exposure apparatuses have been modified tomeet such miniaturization, as well as improvements in a resist process.

The resolving power of an exposure apparatus can be improved by twomethods, that is, a method in which the exposure wavelength isshortened, and a method in which the numerical aperture (NA) of aprojection optical system is enlarged. Generally, the resolution isproportional to the exposure wavelength and it is inversely proportionalto the NA. Besides the improvement of resolution, many attempts havebeen made to keep the depth of focus of a projection optical system.Generally, the depth of focus is proportional to the exposurewavelength, and it is inversely proportional to the square of the NA.Thus, improving the resolution and keeping the depth of focus arecontradictory matters. As an attempt to solve such a problem, a phaseshift method and a FLEX (Focus Latitude Enhancement Exposure) method,for example, have been proposed.

As regards the exposure wavelength, recently, KrF excimer lasers havingan emission wavelength of about 248 nm are prevalently used in place ofi-line of 365 nm. Also, ArF excimer lasers having an emission wavelengthof about 193 nm are currently being developed, as a next generationexposure light source.

From the viewpoint of the production cost of a semiconductor device,further improvements in the throughput of an exposure apparatus havebeen attempted. For example, the power of an exposure light source isenlarged to thereby shorten the exposure time per one shot. Anotherexample is enlarging the exposure area to thereby increase the number ofchips per one shot.

In recent years, in order to meet the requirement of enlargement in chipsize of a semiconductor device, the stream is shifting fromstep-and-repeat type exposure apparatuses (steppers) in which a maskpattern is printed sequentially in association with stepwise motion, tostep-and-scan type exposure apparatuses in which a mask and a wafer arescanningly exposed in synchronism with each other, followed by stepwisemotion to place a subsequent shot. In such step-and-scan type exposureapparatuses, the exposure field has a slit-like shape and, therefore,the exposure area can be enlarged without enlargement in size of theprojection optical system.

Where ultraviolet light is used as an exposure light source, asdescribed above, there may occur a phenomenon that, due to long-perioduse, ammonium sulfate (NH₄) or silicon dioxide (SiO₂) is deposited onthe surface of an optical element disposed on the light path, to causeconsiderable degradation of the optical characteristic. The depositionis produced because of chemical reaction of ammonia (NH₃), sulfurousacid (SO₂) or silicon compound contained in the surrounding ambiencecaused in response to irradiation with ultraviolet light. In order toprevent such deterioration of optical elements, conventionally, thewhole of the light path is purged by use of a clean dry air or an inertgas such as nitrogen.

As regards deep ultraviolet light, particularly, ArF excimer lasershaving a wavelength of about 193 nm, it is known that there are pluralabsorbing bands for oxygen (O₂) in the bandwidth about that wavelength.Also, ozone (O₃) will be produced when oxygen absorbs light, and thisozone acts to increase light absorption, causing considerable decreaseof transmission factor. Additionally, various products, as describedabove, attributable to the ozone will be deposited on the surface of anoptical element, thus causing a decrease of the efficiency of theoptical system.

In consideration of it, in an exposure optical system for projectionexposure apparatuses having a deep ultraviolet light source such as anArF excimer laser, for example, purge means using an inert gas such asnitrogen, for example, may be provided to keep the oxygen density alongthe light path at a low level.

An example of such inert gas purge means for an illumination opticalsystem in a projection exposure apparatus, will be described withreference to FIG. 8.

As illustrated in the drawing, there are an excimer laser 201, and acontainer or housing 202 for the illumination optical system. Further,there are a reticle 203 and mirrors 204, 205 and 206. Denoted at 207 isa beam shaping optical system, and denoted at 208 is an opticalintegrator. Also, there are condenser lenses 209, 210 and 211.

A laser beam emitted by the excimer laser 201 is shaped by the beamshaping optical system 207 into a predetermined beam shape. Thereafter,the light enters the optical integrator 208 and, in response, secondarylight sources (not shown) are produced near the light exit surface ofthe optical integrator 208. The light rays from the secondary lightsources are directed through the condenser lenses 209, 210 and 211 touniformly illuminate the reticle 203. Thus, the arrangement provides aKoehler illumination optical system.

In order to provide an inert gas ambience around the optical elementsdescribed above and along the light path of them, inert gas supply means(not shown) supplies a nitrogen gas, for example, into the housing 202through a gas inlet port 202 a. The thus applied inert gas flows throughthe interior of the illumination optical system. After substitution toremove any residual gas such as atmospheric gas, for example, the inertgas is discharged outwardly through a gas outlet port 202 b, by gasdischarging means (not shown).

The gas supply quantity may be controlled so as to minimize thesubstitution time by the inert gas, to thereby increase the systemthroughput, or minimize the consumption quantity of the inert gas aftersubstitution, to thereby decrease the system running cost (JapaneseLaid-Open Patent Application, Laid-Open No. 216000/1994).

On the other hand, a currently prevailing illumination method is avariation illumination method (e.g., Japanese Laid-Open PatentApplication, Laid Open No. 204114/1994) wherein the distribution of thesecondary light source as described above is changed in various ways.This is to accomplish both a high resolution and a large depth of focus.In order that the illumination condition is made variable, many opticalelements of an illumination optical system should be madeinterchangeable. With the above-described inert gas substitution method,on that occasion, it is very difficult to forcibly substitute the insidespace of a mechanism (barrel) for holding optical elements to beinterchanged. Particularly, in a case where an ArF excimer laser havingan emission wavelength about 193 nm is used, there is a problem, asdescribed, that the light absorption occurs due to any oxygen remainingalong the light path which causes a serious decrease of opticalefficiency. Therefore, forcible substitution of the interior of themovable barrel, if desired, needs a complicated structure for the gasflow passageway, and it causes an increase of the system cost as well asprolongation of the time for completion of the substitution whichresults in a decrease of the system throughput.

SUMMARY OF THE INVENTION

It is accordingly an object of the present invention to accomplishreduction of a substitution time to an inert gas ambience along anexposure light path, still with a minimum cost, and thereby to increasethe system throughput.

In accordance with an aspect of the present invention, there is providedan exposure apparatus, comprising: a light source; at least one (one ortwo or more) housing for accommodating therein an optical elementdisposed along an exposure light path extending from said light sourceto a substrate; first substitution means for substituting the interiorof said housing with an inert gas ambience; and second substitutionmeans for substituting the interior of a holding mechanism for holdingthe optical element accommodated in said housing, with an inert gasambience.

The second substitution means may preferably include control means forcontrolling an inert gas supply quantity in accordance with the state ofsubstitution of the inert gas ambience inside said holding mechanism andthe state of substitution of the inert gas ambience inside said housing.

Each of the first and second substitution means may include controlmeans for controlling an inert gas supply quantity, each control meansbeing operable independently to set an inert gas supply quantity and acontrol operation timing.

The holding mechanism may comprise a barrel for movably holding saidoptical element in said housing.

The housing may accommodate therein the whole of or a portion of anillumination optical system for directing light from said light sourceto a reticle, and the holding mechanism may movably hold an opticalelement which may serve to variably or interchangeably set anillumination condition of said illumination optical system.

The housing may comprise a barrel for a projection optical system, andthe holding mechanism may movably hold a lens inside said projectionoptical system, for variably or interchangeably setting an opticalcharacteristic of said projection optical system.

The light source may comprise a light source of one of deep ultravioletlight and an excimer laser.

In accordance with another aspect of the present invention, there isprovided a device manufacturing method including a process for producinga device by use of an exposure apparatus as recited above.

In accordance with a further aspect of the present invention, there isprovided an exposure method, comprising the steps of: preparing at leastone housing for accommodating therein an optical element disposed alongan exposure light path extending from a light source to a substrate;substituting, by use of first substitution means, the interior of thehousing with an inert gas ambience; and substituting, by use of secondsubstitution means, the interior of a holding mechanism for holding theoptical element accommodated in the housing, with an inert gas ambience,whereby the inside of the housing is substituted with an inert gasambience.

In the exposure method described above, the second substitution meansmay be used to control an inert gas supply quantity in accordance withthe state of substitution of the inert gas ambience inside the holdingmechanism and the state of substitution of the inert gas ambience insidethe housing.

Alternatively, each of the first and second substitution means mayinclude control means for controlling an inert gas supply quantity, eachcontrol means being operable independently to set an inert gas supplyquantity and a control operation timing.

Further, the holding mechanism may comprise a barrel for movably holdingthe optical element in the housing.

In the exposure method described above, the housing may accommodatetherein the whole of or a portion of an illumination optical system fordirecting light from the light source to a reticle, and the holdingmechanism may movably hold an optical element which may serve tovariably or interchangeably set an illumination condition of theillumination optical system.

In the exposure method described above, the housing may comprise abarrel for a projection optical system, and wherein the holdingmechanism movably holds a lens inside the projection optical system, forvariably or interchangeably setting an optical characteristic of theprojection optical system.

In the exposure method described above, the light source may comprise alight source of one of deep ultraviolet light and an excimer laser.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a projection exposure apparatus accordingto an embodiment of the present invention.

FIG. 2 is a schematic view for explaining scan exposure to be made inthe exposure apparatus of FIG. 1.

FIG. 3 is a schematic view for explaining details of an input lensportion in the exposure apparatus of FIG. 1.

FIG. 4 is a schematic and diagrammatic view of an inert gas supplyingand discharging system in the exposure apparatus of FIG. 1.

FIGS. 5A, 5B, 5C, 5D, 5E and 5F are graphs, respectively, for explaininga nitrogen flow rate and a change in the state of nitrogen substitution,in the exposure apparatus of FIG. 1.

FIG. 6 is a schematic and diagrammatic view of a modified example of thegas supplying and discharging system of FIG. 4.

FIG. 7 is a schematic view of a projection exposure apparatus accordingto another embodiment of the present invention.

FIG. 8 is a schematic view of a conventional projection exposureapparatus.

FIG. 9 is a flow chart of microdevice manufacturing processes.

FIG. 10 is a flow chart for explaining details of a wafer process in theprocedure shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be describedwith reference to the accompanying drawings.

First Embodiment

FIG. 1 shows a first embodiment of the present invention.

Denoted in the drawing at 1 is a deep ultraviolet light source such asan ArF excimer laser, for example, and denoted at 2 is a mirror. Thereare a beam shaping optical system 3 and an input lens 4. Further, thereare an imaging lens 5, a mirror 6, an optical integrator 7, a stopper 8,a condenser lens 9, and a blind 10. Denoted at 11 is another condenserlens, and denoted at 12 is a mirror. Denoted at 13 is a condenser lens.

A laser beam emitted by the ArF excimer laser 1 is directed via themirror 2 to the beam shaping optical system 3, by which the light isshaped into a predetermined beam shape. Thereafter, the light goes viathe input lens 4, the imaging lens 5 and the mirror 6, and it enters theoptical integrator 7 which comprises small lenses arrayedtwo-dimensionally. In response, secondary light source images areproduced near the light exit surface 7 a of the optical integrator 7.There is the stopper 8 disposed adjacent the plane where the secondarylight sources are produced. Thus, by changing the stopper 8 by anotherin association with interchanging the input lens 4, a desireddistribution of secondary light sources can be produced. Denoted at 14and 15 are actuators for the switching drive of the input lens and thestopper, respectively.

The light from the secondary light sources is collected by the condenserlens 9. Adjacent a plane orthogonal to the optical axis and containingthe point of light convergence defined by the condenser lens, there isthe blind 10 disposed which functions to determine the illuminationrange for a mask 16. The light from the light convergence plane goes viathe condenser lenses 11 and 13 and the mirror 12, such that a Koehlerillumination optical system for illuminating the mask 16 uniformly isprovided.

The whole illumination optical system described above is accommodated ina container or housing 17, so that they are isolated against gascommunication with the outside atmosphere.

Denoted at 18 is a mask stage, and denoted at 19 is a mirror. Denoted at20 is an interferometer, and denoted at 22 is a projection opticalsystem. Denoted at 23 is a wafer, and denoted at 24 is a wafer chuck.Denoted at 25 is a wafer stage, and denoted at 26 is a mirror. Denotedat 27 is an interferometer.

As shown in FIG. 2, the illumination optical system described aboveserves to illuminate a portion of a pattern 28 formed on the mask 16,with slit-like light 29 (i.e., slit illumination). The portion of thepattern 28 is projected by the projection optical system 22 onto thewafer 23, in a reduced scale.

Here, the mask 16 and the wafer 23 are scanningly moved relative to theprojection optical system 22 and the slit-like illumination 29, inopposite directions as depicted by arrows in the drawing, at a speedratio corresponding to the reduction magnification of the projectionoptical system 22, while on the other hand multiple-pulse exposure basedon the pulse light from the ArF excimer laser is repeated. In thismanner, the whole pattern 28 on the mask 16 can be transferred to asingle or plural chip regions on the wafer 23.

Referring back to FIG. 1, denoted at 18 is a mask stage for holding amask 16 thereon. It can be scanningly moved in a direction of an arrowC, by means of a driving system (not shown). Denoted at 19 is a mirrorfixedly mounted on the mask stage 18, and denoted at 20 is a laserinterferometer for detecting the movement speed of the mask stage 18.Denoted at 24 is a wafer chuck for holding a wafer 23 thereon, anddenoted at 25 is a wafer stage for holding the wafer chuck 24 thereon.It can be scanningly moved in a direction of an arrow D, by means of adriving system (not shown). Denoted at 26 is a mirror fixedly mounted onthe wafer stage 25, and denoted at 27 is a laser interferometer fordetecting the movement speed of the wafer stage 25.

Denoted at 31 is inert gas supplying means which operates, in thisembodiment, to provide a gas supply to the housing 17 of theillumination optical system as well as to two locations in theprojection optical system 22, as illustrated. The gas supply to thehousing 17 of the illumination optical system is based on a supplysystem 32, connected to a portion near the laser emission end of the ArFexcimer laser 1. Thus, the supplied gas flows along the laser light pathwhile passing the optical elements sequentially, so that the gas insidethe housing 17 is discharged outwardly. Finally, the gas is dischargedoutwardly, from a portion near the condenser lens 13 and through anevacuation system 33, by means of evacuation means 34.

The supply of an inert gas to the projection optical system 22 is madethrough a supply system 35 connected at an end of the projection opticalsystem 22. The gas passes inside optical elements (not shown)sequentially, and it is discharged outwardly from the other end andthrough an evacuation system 36, by use of the evacuation means 34.

Denoted at 37 is another inert gas supplying means which operates, inthis embodiment, to provide gas supply to the input lens 4, separately,with use of a supply system 38.

FIG. 3 illustrates details of the input lens 4 and components around it.Denoted in the drawing at 41 a-41 b are optical elements, among theoptical elements of the beam shaping optical system 3, described withreference to FIG. 1. Denoted at 42 is a case, and denoted at 43 a and 43b are spacers. Denoted at 44 is a holding ring, and denoted at 45 a-45 bare pipings. Denoted at 46 is a container or housing, and denoted at 47is a gas deflecting plate.

Denoted at 48 a and 48 b are optical elements, among the opticalelements of the imaging lens system 5 having been described withreference to FIG. 1. Denoted at 49 is a case, and denoted at 50 is aspacer. Denoted at 51 a and 51 b are pipings.

Denoted at 14 is an actuator having been described with reference toFIG. 1. Denoted at 52 is a housing, and denoted at 53 is a shaft.Denoted at 54 is a sealing member, and denoted at 55 is a bearing.Denoted at 56 is a rotary plate. Denoted at 57 a and 57 b are firstinput lens elements, and denoted at 58 is a barrel. Denoted at 59 a and59 b are holding rings, and denoted at 60 is a gas outlet port. Denotedat 61 a and 61 b are second input lens elements, and denoted at 62 is abarrel. Denoted at 63 a and 63 b are holding rings, and denoted at 64 isa gas outlet port.

The functions and operations of these components will be described withreference to FIG. 3.

As has been described with reference to FIG. 1, the light beam passingthrough the beam shaping optical system is shaped into a predeterminedbeam shape. The components of this optical system at a trailing endthereof are the optical elements 41 a and 41 b shown in FIG. 3. Theseoptical elements 41 a and 41 b as well as the other optical elements(not shown) which are components of the beam shaping optical system areall accommodated in the case 42. In this embodiment, these elements aremounted in an order of the spacer 43 a, the optical element 41 a, thespacer 43 b and the optical element 42 b. Also, these elements are heldfixed by means of the holding ring 44 which is thread-engaged with theinside circumferential surface of the case 42, at an end thereof. Thecase 42 and the spacers 43 a and 43 b are provided with gascommunication bores. Thus, the inert gas flowing along the light path,from the light source side, reaches the optical element 43 a portion asdepicted by an arrow A in the drawing. Thereafter, the gas flows throughthe communication bores and the pipings 45 a and 45 b, so that it isdirected into the housing 46 while performing inert gas substitution ofthe space for the optical elements 41 a and 41 b. The deflecting plate47 is disposed so that the inert gas thus introduced can flow throughoutthe housing 46 without stagnation. The inert gas passed through thehousing 46 is directed by means of a piping 51 a to the space betweenthe optical elements 48 a and 48 b and, after inert gas substitution ofthat space, it flows through a piping 51 b toward-a succeeding opticalsystem (not shown).

These optical elements 48 a and 48 b as well as the other opticalelements (not shown) which are components of the imaging lens system areall accommodated in the case 49. In this embodiment, these elements aremounted in an order of the optical element 48 a, the spacer 50 and theoptical element 48 b. Also, these elements are held fixed inside thecase 49, by use of fixing means (not shown). The connection between thecase 42 and the housing 46 as well as the connection between the housing46 and the case 42 are gas-tightly closed and isolated against gascommunication with the outside atmosphere. Therefore, there occurs nooutward leakage of the inert gas.

The first input lens elements 57 a and 57 b are mounted at opposite endsof the barrel 58, and they are held fixed by means of the holding rings59 a and 59 b each being thread-engaged with the inside circumferentialsurface of the barrel 58, at an end thereof. Similarly, the second inputlens elements 61 a and 61 b are mounted at opposite ends of the barrel62, and they are held fixed by means of the holding rings 63 a and 63 beach being thread-engaged with the inside circumferential surface of thebarrel 62, at an end thereof. The first input lens and the second inputlens elements are provided by different optical elements. Thus, byselectively and interchangeably inserting either the first or secondinput lens into the laser light path, the intensity distribution of thelaser beam impinging on the optical integrator 7 through the imaginglens 5 of FIG. 1, can be controlled.

The interchanging mechanism for the input lenses will now be describedin detail.

The barrels 58 and 62 are fixedly mounted on the rotary plate 56. Therotary plate 56 is connected to the actuator 14 through the shaft 53.Further, the shaft 53 is supported by the housing 52 through the bearing55. Also, the actuator 14 is fixedly mounted on a holder, not shown. Thepositioning of the first and second input lenses is performed by usingan angular sensor (not shown) accommodated in the actuator.

The housing 52 is provided with a gas inlet port 65 to which a gassupply is made separately by the inert gas supplying means 37 shown inFIG. 1. An inert gas is thus supplied as depicted by an arrow B, and itis directed to an inside circumferential groove 66 which is formed inthe inside circumferential surface of the housing 52 and which iscommunicated with the inlet port 65.

The shaft 53 is provided with a gas communication bore 67 beingcommunicated with the groove 66. Thus, even when the shaft 53 rotates,the communication with the groove 66 is kept. There is a sealing member54 as illustrated, between the shaft 53 and the housing 52, such thatrotational motion can be made without leakage of inert gas in thecommunication between the groove 66 and the bore 67.

The gas communication bore 67 is further communicated with acommunication bore 68 which is formed in the rotary plate 56. Thus,inert gases can be introduced through the communication bores 69 and 70of the barrels 58 and 62, respectively, into the barrels 58 and 62,respectively. The gas having substituted the space between the firstinput lens elements 57 a and 57 b is discharged from a gas outlet port60, while the gas having substituted the space between the second inputlens elements 61 a and 61 b is discharged from a gas outlet port 64,respectively, both being directed into the housing 46.

As compared with the gas flow rate as supplied from the inert gas supplymeans 31 of FIG. 1 (arrow A), the gas flow rate as supplied from theinert gas supply means 37 of FIG. 1 (arrow B) is very small. Namely,while the gas of arrow A should function to perform the substitution ofthe inside of the housing 17 for the whole illumination optical systemof FIG. 1, the gas of arrow B is used for the substitution of only theinside of the barrels 58 and 62 of the first and second input lenses.Thus, as compared with the inside volume of the housing 17, the insidevolumes of the barrels 58 and 62 are very small. For this reason, thereis substantially no possibility that the flow of gas discharged from theoutlet ports 60 and 64 applies a large adverse influence to the flow ofgas along the arrow A to cause a decrease of substitution efficiency.However, as regards the shape of the discharging ports 60 and 64, itshould preferably be determined so as not to make the gas flowthroughout the housing 46, unstable.

Details of the inert gas supply means 31 and 37 shown in FIG. 1 will nowbe described, with reference to FIG. 4.

FIG. 4 is a block diagram of a system, from inert gas supply means tounits to which gases should be supplied. Denoted at 81 is a gas supplyline which is connected to a supply source (not shown) of nitrogen(inert gas). This line is forked into two, i.e., one connected to theinert gas supply means 31 and another connected to the inert gas supplymeans 37.

The inside structure of the inert gas supply means 31 will be describedfirst. The gas supply line 81 is further separated into lines 82 and 83.The line 82 is connected to a first electromagnetic valve 84 and, afterpassing through a first pressure gauge 85, it is branched and connectedto throttle valves 86 and 87, respectively. The gas flow rate settingfor the throttles 86 and 87 will be described later. The throttle 86 isconnected to the supply system 32, while the throttle 87 is connected tothe supply system 35.

On the other hand, the line 83 is connected to a second electromagneticvalve 88 and, after passing through a second pressure gauge 89, it isbranched and connected to throttle valves 90 and 91, respectively. Thethrottle 90 is connected to the supply system 32, while the throttle 91is connected to the supply system 35.

Next, the inside structure of the inert gas supply means 37 will bedescribed.

The line branched from the gas supply line 81 is connected to a thirdelectromagnetic valve 92 and, after passing through a third pressuregauge 93, it is connected to a throttle valve 94.

As has been described with reference to FIG. 1, the supply system 32 isconnected to the housing 17 which accommodates the whole illuminationoptical system therein, and, through the gas discharging system 33, itis connected to the gas evacuation means 34. Also, the supply system 35is connected to the projection optical system 22 and, through the gasdischarging system 36, it is connected to the evacuation means 34. Thethrottle valve 94 is connected to the input lens 4 disposed inside thehousing 17 for the illumination optical system, and the gas from theinput lens 4 is discharged through the housing 17 and through thedischarging system 33, into the evacuation means 34.

The evacuation means 34 is, in turn, connected to an evacuationinstrument (not shown) through an evacuation line 95.

The settings and operations of the components will be described below,in conjunction with FIG. 4.

The supply of nitrogen starts as the first and third electromagneticvalves 84 and 92 are opened in response to signals from a controller(not shown). Here, the second electromagnetic valve 88 is kept closed.The pressure gauges 85 and 93 are connected to the controller (notshown), and they function to check whether a predetermined pressure isreached as the first and third electromagnetic valves 84 and 92 areopened. If any disorder occurs in the gas supply system and thepredetermined pressure is not accomplished, a signal of malfunction isapplied to the controller, in response to which an appropriate reactionsuch as interruption of operation is made.

The throttles 86 and 87 are set to their optimum flow rate levels sothat the gas, such as atmospheric air, inside the projection opticalsystem can be substituted with nitrogen, in a necessary and shortesttime.

As regards the throttle 94, the flow rate is set to such a level thatthe substitution of the inside of the input lens can be completed beforethe substitution of the housing 17 is accomplished as described above,thus substantially enabling the light emission of the ArF excimer laser.

The unshown controller operates to close the first and thirdelectromagnetic valves 84 and 92 after an elapse of a predetermined timeand, on the other hand, it operates to open the second electromagneticvalve 88. The pressure gauge 89 detects whether a predetermined gaspressure is reached or not as the second electromagnetic valve 88 isopened. If any disorder occurs in the gas supply system and thepredetermined pressure is not accomplished, a signal of malfunction isapplied to the controller, in response to which an appropriate reactionsuch as interruption of operation is made.

Since at that time the substitution of the interiors of the housing 17and the projection optical system 22 with a nitrogen gas has beenaccomplished, nitrogen may thereafter be supplied at a level thatmaintains this substitution state. Thus, when the set flow rate of thethrottle 86 is denoted by Q₈₆, and similarly the set flow rates of thethrottles 87, 90 and 91 are denoted by Q₈₇, Q₉₀ and Q₉₁, respectively,then there may be relations of Q₉₀<Q₈₆ and Q₉₁<Q₈₇.

FIGS. 5A-5F schematically illustrate the nitrogen flow rate and changesin the state of nitrogen substitution, in accordance with the proceduredescribed above.

Among these drawings, FIG. 5A shows the quantity of nitrogen supply tothe housing 17, wherein the axis of abscissa denotes time and the axisof ordinate denotes the nitrogen flow rate. At time t₀, the nitrogensupply starts. The flow rate is at Q₈₆ and is constant. At time t_(i),the nitrogen flow rate is changed to Q₉₀. FIG. 5B shows changes inoxygen density, during this procedure, as an index of the state ofnitrogen substitution inside the housing 17. The axis of abscissadenotes time, and the axis of ordinate denotes the oxygen density withinthe housing 17. The initial oxygen density at the nitrogen supply starttime (t₀) is depicted as a level d₀, and the oxygen density with whichthe exposure process can be started substantially without anyinconveniences is depicted as a level d₁. If the time where the oxygendensity reaches the level d₁ is t₂, the timing for changing the nitrogenflow rate may be set to satisfy a relation that t₂≦t₁.

FIG. 5C shows the quantity of nitrogen supply to the input lens 4, andFIG. 5D shows changes in the oxygen density inside the input lens. InFIG. 5C, the nitrogen supply starts at time t₀. The flow rate is at alevel Q₉₄, and it is constant. At time t₃, the nitrogen supply isinterrupted. In FIG. 5D, the time where the oxygen density inside theinput lens 4 reaches a level d₁ with which the exposure process can bestarted substantially without any inconveniences is denoted at t₄. Thetiming for changing the nitrogen flow rate may be set to satisfy arelation t₄≦t₃. It is seen from FIG. 5C that, even if the nitrogensupply is interrupted after time t₃, the ambience surrounding the inputlens 4 is the nitrogen ambience because it is placed inside the housing17, and that there does not occur undesirable degradation of thenitrogen substitution level.

FIG. 5E shows the quantity of nitrogen supply to the projection opticalsystem 22, and FIG. 5F shows changes in oxygen density inside theprojection optical system 22. In FIG. 5E, the nitrogen supply starts attime t₀. The flow rate is at a level Q₈₇, and it is constant. At timet₁, the flow rate of nitrogen is changed to a level Q₉₄. In FIG. 5F, thetime where the oxygen density inside the projection optical system 22reaches a level d₁ with which the exposure process can be startedsubstantially without any inconveniences is denoted at t₅. The timingfor changing the nitrogen flow rate may be set to satisfy a relationt₅≦t₁.

As described above, if the time until a predetermined nitrogensubstitution level is accomplished is predetected, the switching timingfor the electromagnetic valves 86, 87, 90, 91 and 92 shown in FIG. 4 canbe set in the controller, as desired. Further, if it is desired to bestoptimize the timing for changing the nitrogen flow rate to therebyreduce the nitrogen consumption, appropriate substitution levelmonitoring means such as an oxygen density gauge, for example, may bedisposed inside the housing 17, the input lens 4 and/or the projectionoptical system 22, so that the nitrogen flow rate may be changed by thecontroller, in accordance with an output of the monitor.

Further, while the description has been made above with reference to anexample where the nitrogen supply to the input lens 4 is interrupted orstopped at a predetermined time, if it is desired to continue supply ofa very small amount of nitrogen, rather than stopping the nitrogensupply, a structure such as shown in FIG. 6 may be used. In FIG. 6,components corresponding to those of FIG. 4 are denoted by likereference numerals. A description thereof will be omitted here.

In FIG. 6, denoted at 96 is a fourth electromagnetic valve, and denotedat 97 is a fourth pressure gauge. Denoted at 98 is a throttle valve. Inthis example, the nitrogen flow rate Q₉₄ through the throttle 94 and thenitrogen flow rate Q₉₈ through the throttle 98 may be placed in arelation Q₉₈<Q₉₄. As the third electromagnetic valve 92 is closed by thecontroller (not shown), the fourth electromagnetic valve 96 is opened,whereby a predetermined amount of nitrogen is supplied to the input lens4.

Second Embodiment

FIG. 7 shows an embodiment wherein, in addition to the structure of theembodiment shown in FIG. 1, a system for separate nitrogen supply to aspace for a particular lens inside the projection optical system 22 isadded. In FIG. 7, components corresponding to those of FIG. 1 aredenoted by like reference numerals. A description thereof will beomitted here.

The projection optical system 22 has such a structure to be describedbelow.

In FIG. 7, denoted at 101 a-101 g are lenses, and denoted at 102 a-102 eare lens holders. Denoted at 103 is a group holder. Denoted at 104 is acontainer or housing for the projection optical system, and denoted at105 is an actuator. Denoted at 106 is a connector.

The lens 101 a is held by the lens holder 102 a. Similarly, the lenses101 d, 101 e, 101 f and 101 g are held by the lens holders 102 b, 102 c,102 d and 102 e, respectively. Also, the lenses 101 b and 101 c are heldby the group holder 103, and they can be moved along an optical axisdirection by means of the actuator 105, for correction of aberration ofthe projection optical system 22. The actuator 105 is connected to thegroup holder 103, through the connector 106.

In this embodiment, the inert gas supply means 31 operates to supply agas into the projection optical system housing 104, at a portion nearthe top end of the housing. Through gas communication bores formed inthe lens holders 102 b, 102 c and 102 d, nitrogen substitution isperformed sequentially to the lens spaces. Finally, the gas isdischarged to the evacuation means 34. Further, the inert gas supplymeans 37 functions to supply nitrogen into the group holder 103. Afternitrogen substitution of the space between the lenses 101 b and 101 c isaccomplished, the gas is discharged into the housing 104 through a gascommunication bore formed in the group bolder 103. Subsequently, likethat described above, the gas passes sequentially through the lensspaces through gas communication bores formed in the lens holders, andfinally it is discharged to the evacuation means 34. As has beendescribed with reference to the embodiment of FIG. 1, also in thisembodiment, the flow rate of nitrogen from the inert gas supply means 37is very small as compared with the nitrogen flow rate from the inert gassupply means 31. For this reason, there is substantially no possibilitythat a gas discharged from the group holder 103 disturbs the flow ofnitrogen inside the housing 104.

As regards the nitrogen supply to the group holder 103, the supply maybe stopped in a predetermined time period, like the first embodiment.Alternatively, the flow rate may be changed to a low level, rather thanstopping the same.

While two embodiments of the present invention have been describedabove, the object to which an inert gas should be supplied separatelyfrom the inert gas supply means 37 is not limited to an optical elementwhich is to be driven, as described. For example, the separate inert gassupply may be made to any location where inert gas substitution is noteasy because of the disposition of an optical element or elements or ofany structure around it.

Further, while the foregoing description has been made with reference toexamples where nitrogen is used as an inert gas, any other inert gas mayof course be used, with a result of similar advantageous effects of theinvention.

Third Embodiment

Next, an embodiment of a semiconductor device manufacturing method whichuses an exposure apparatus such as described above, will be explained.

FIG. 9 is a flow chart of a procedure for the manufacture ofmicrodevices such as semiconductor chips (e.g., ICs or LSIs), liquidcrystal panels, CCDs, thin film magnetic heads or micro-machines, forexample.

Step 1 is a design process for designing a circuit of a semiconductordevice. Step 2 is a process for making a mask on the basis of thecircuit pattern design. Step 3 is a process for preparing a wafer byusing a material such as silicon. Step 4 is a wafer process (called apre-process) wherein, by using the so prepared mask and wafer, circuitsare practically formed on the wafer through lithography. Step 5subsequent to this is an assembling step (called a post-process) whereinthe wafer having been processed by step 4 is formed into semiconductorchips. This step includes an assembling (dicing and bonding) process anda packaging (chip sealing) process. Step 6 is an inspection step whereinan operation check, a durability check and so on for the semiconductordevices provided by step 5, are carried out. With these processes,semiconductor devices are completed and they are shipped (step 7).

FIG. 10 is a flow chart showing details of the wafer process.

Step 11 is an oxidation process for oxidizing the surface of a wafer.Step 12 is a CVD process for forming an insulating film on the wafersurface. Step 13 is an electrode forming process for forming electrodesupon the wafer by vapor deposition. Step 14 is an ion implanting processfor implanting ions to the wafer. Step 15 is a resist process forapplying a resist (photosensitive material) to the wafer. Step 16 is anexposure process for printing, by exposure, the circuit pattern of themask on the wafer through the exposure apparatus described above. Step17 is a developing process for developing the exposed wafer. Step 18 isan etching process for removing portions other than the developed resistimage. Step 19 is a resist separation process for separating the resistmaterial remaining on the wafer after being subjected to the etchingprocess. By repeating these processes, circuit patterns are superposedlyformed on the wafer.

With these processes, high density microdevices can be manufactured at alower cost.

In accordance with the embodiments of the present invention as describedhereinbefore, inert gas substitution along an exposure light path can beperformed satisfactorily. Consequently, the present invention canprovide an exposure apparatus of higher efficiency and a higherthroughput.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purposes of the improvements or the scope of thefollowing claims.

What is claimed is:
 1. An exposure apparatus having two optical elementsfor directing light from a light source to a member to be exposed, saidapparatus comprising: first gas supplying means for supplying a firstgas into a first space partitioned by the two optical elements; ahousing that defines a second space substantially surrounding the firstspace; and second gas supplying means for supplying a second gas intothe second space, wherein a gas discharged from the first space isintroduced into the second space.
 2. An apparatus according to claim 1,wherein a gas ambience to be produced in the first space is an inert gasambience.
 3. An apparatus according to claim 1, wherein a gas ambienceto be produced in the second space is an inert gas ambience.
 4. Anapparatus according to claim 1, further comprising an illuminationoptical system for illuminating an original with light from the lightsource, wherein said illumination optical system has said two opticalelements.
 5. An apparatus according to claim 1, further comprising (i)an illumination optical system for illuminating an original with lightfrom the light source, said illumination optical system having said twooptical elements, (ii) a projection optical system for directing lightfrom the original to the member to be exposed, and (iii) third gassupplying means for supplying an inert gas into said projection opticalsystem.
 6. An apparatus according to claim 5, wherein said second gassupplying means functions also as said third gas supplying means.
 7. Adevice manufacturing method, comprising the steps of: exposing a memberto be exposed, by use of an exposure apparatus as recited in claim 1;and developing the exposed member.
 8. An illumination optical system forilluminating an original with light from a light source, saidillumination optical system comprising: a housing for surrounding atleast a portion of said illumination optical system; first gas supplyingmeans for supplying a first inert gas to said housing; and second gassupplying means for supplying a second inert gas into an inside spacepartitioned by two optical elements disposed inside said housing,wherein a gas discharged out of the inside space is introduced into saidhousing.
 9. An illumination optical system according to claim 8, whereinthe first inert gas and the second inert gas are the same inert gas. 10.An exposure apparatus comprising: an illumination optical system asrecited in claim 8; and a projection optical system for directing lightfrom the original to a member to be exposed.
 11. A device manufacturingmethod, comprising the steps of: exposing a member to be exposed, by useof an exposure apparatus as recited in claim 10; and developing theexposed member.